The present invention relates to a potential detector to detect an electric potential output from a high voltage generator, etc., that has reached a certain level in a semiconductor integrated circuit.
FIG. 1 shows a known potential detector 90. The detector 90 consists of resistors R1 and R2 connected in series between a terminal 91 to be detected and a ground terminal VSS, and a comparator CMP to compare a potential at a node at which the resistors R1 and R2 are connected together with a reference potential Vref.
The potential at the node of the resistors R1 and R2 is obtained as V1·R2/(R1+R2) where V1 is a potential at the terminal 91. The comparator CMP outputs a high-level detection signal when the potential at the node exceeds the reference potential Vref.
The potential detector 90 is used, for example, for detecting an output potential Vout of a high voltage generator used in a semiconductor circuit such as a non-volatile semiconductor memory.
FIG. 2 shows an example where the potential detector 90 is used for detecting a potential Vout appearing at an output terminal 91 of a high voltage generator 901 such as a charge pump. The high voltage generator 901 is driven by clocks generated by an oscillator 902 such as a ring oscillator.
The potential detector 90 outputs a detection signal Dout when the potential Vout appearing at the output terminal 91 of the high voltage generator 901 reaches a certain potential to deactivate a gate 903 that has fed clocks generated by the oscillator 902 to the high voltage generator 901. The high voltage generator 901 then stops, so that the boosted output Vout is kept at a constant level, as illustrated in FIG. 3A.
The known potential detector generates a potential by the series-connected resistors, which is compared with a reference potential. A current always flows through the resistors R1 and R2 for generating the potential. The high voltage generator 901 thus requires a drive performance high enough for accepting a current consumed by the resistors R1 and R2. The drive performance of the high voltage generator is decided according to the resistance of the resistors R1 and R2 when a load capacitance to be driven by the high voltage generator is relatively small. This requires drive performance for the high voltage generator higher than that for the high voltage generator to drive the load itself, which is not practical in view of power consumption and circuit integration.
A high voltage generator having unnecessarily high drive performance will generate a potential boosted to a high level during a response time of a potential detector. This results in a large variation in boosted output Vout against an anticipated level, as illustrated in FIG. 3B, with difficulty in obtaining a constantly boosted potential.
The larger the resistance of the resistors R1 and R2 for avoiding such potential variation, the larger the parasitic capacitance to the resistors. This results in a large delay of change in output potential of the high voltage generator, and further a large delay time required for the output potential to be transferred to the input terminal of the comparator CMP. Change in output potential of the high voltage generator illustrated in FIG. 3C does not have an abrupt potential increase such as shown in FIG. 3B, however, exhibits a slow response. This also results in unstably un-converted potential output.